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rshd(8) System Manager's Manual rshd(8) NAME rshd - The remote shell server SYNOPSIS rshd [-aln] FLAGS The addresses for the hostname are requested, verifying that the name and address correspond. Prevents the ruserok command from doing any validation based on the user's .rhosts file, unless the user is the su- peruser. Disables transport-level, keep-alive messages. SECURITY NOTE This security-sensitive command uses the SIA (Security Integration Ar- chitecture) routine as an interface to the security mechanisms. See the matrix.conf4 reference page for more information. DESCRIPTION The rshd daemon is the server for the rcmd(3) routine and, conse- quently, for the rsh(1) program. The server provides remote execution facilities with authentication based on privileged port numbers from trusted hosts. The rshd daemon listens for service requests at the port indicated in the cmd service specification; see services(4). When a service request is received, the following protocol is initiated: The server checks the client's source port. If the port is not in the range 512 to 1023, the server aborts the connection. The server reads bytes from the socket up to a null (`\0') byte. The resultant string is interpreted as an ASCII number, base 10. If the number received in step 2 is nonzero, it is interpreted as the port number of a secondary stream to be used for the stderr option. A second connection is then created to the speci- fied port on the client's machine. The source port of this second con- nection is also in the range 512 to 1023. The server checks the client's source address and requests the corresponding hostname (see gethostbyaddr(3), hosts(4), and named(8)). If the hostname cannot be determined, the dot-notation representation of the host address is used. If the hostname is in the same domain as the server (according to the last two components of the domain name), or if the -a flag is given, the addresses for the hostname are requested, verifying that the name and address correspond. If address verification fails, the con- nection is aborted with the message Host address mismatch. A null-ter- minated username of at most 16 bytes is retrieved on the initial socket. This username is interpreted as the user identity on the client 's machine. A null-terminated username of at most 16 bytes is retrieved on the initial socket. This username is interpreted as a user identity to use on the server's machine. A null-terminated com- mand to be passed to a shell is retrieved on the initial socket. The length of the command is limited by the upper bound on the size of the system's argument list. The rshd daemon then validates the user using ruserok(3), which uses the file /etc/hosts.equiv and the .rhosts file found in the user's home directory. The -l flag prevents ruserok(3) from doing any validation based on the user's .rhosts file, unless the user is the superuser. A null byte is returned on the initial socket and the command line is passed to the normal login shell of the user. The shell inherits the network connections established by rshd. Transport-level, keep-alive messages are enabled unless the -n flag is present. The use of keep-alive messages allows sessions to be timed out if the client crashes or becomes unreachable. CAUTIONS The authentication procedure used here assumes the integrity of each client machine and the connecting medium. This is insecure, but is useful in an open environment. DIAGNOSTICS Except for the last diagnostic message listed, all diagnostic messages are returned on the initial socket, after which any network connections are closed. An error is indicated by a leading byte with a value of 1 (0 is returned in step 9 above upon successful completion of all the steps prior to the execution of the login shell). The name of the user on the client's machine is longer than 16 characters. The name of the user on the remote machine is longer than 16 characters. The command line passed exceeds the size of the argument list (as configured into the system). No password file entry for the username existed. The chdir command to the home directory failed. The authentication proce- dure previously described failed. The pipe needed for the stderr op- tion, but it was not created. A fork by the server failed. The user's login shell could not be started. This message is returned on the con- nection associated with the stderr option, and is not preceded by a flag byte. FILES Specifies the command path RELATED INFORMATION Commands: rsh(1) Functions: rcmd(3), ruserok(3) delim off rshd(8)